This invention refers to a procedure for the preparation of aromatic compounds of titanocene. More particularly it refers to a procedure of synthesis of bis(aryl) and bis(cyclopentadienyl) titanium derivatives via the Grignard reagent.
The alkyl and aryl compounds derived from titanocene are very useful in numerous organic reactions, for instance as catalysts for the polymerisation and hydrogenation of polymers. The large number of publications (U.S. Pat. No. 2,952,670 (1960); Gevaert-Agfa, Neth. Patent 6,603,202 (1966); Natta, G., et al, Chim. Ind. (Milan) 39, 1032 (1957); U.S. patent application Ser. No. 3,000,870 (1958); Ryabov, A. V., et al., Vysokomol. Soedin, Ser. Bll, 49 (1969)), evidences the interest aroused by bis(cyclopentadienyl) bis(phenyl) titanium as catalyst together with titanium tetrachloride or an alkyl aluminium compound for the polymerisation of ethylene.
On the other hand, the hydrogenation catalyst activity of polymers of bis(cyclopentadienyl) bis(alkylphenil)titanium described in patent GB 2159819 or bis (cyclopentadienyl) bis(alcoxyphenyl) titanium claimed in patent EP 0 601 953 is well known.
The efforts to prepare organotitanium compounds with "sgr" bonds date back to more than a century ago, but it was not until 1952 that Herman et al., J. Amer., Chem. Soc. 74,2693 (1952) synthesised the first organotitanium compound. Somewhat latter, in 1954 the first bis(aryl) derivatives of bis(cyclopentadienyl) titanium were isolated by reaction of titanocene dichloride and the corresponding aryl lithium salt, being in this way that L. Summers et al, (J. Amer., Soc. 76, 2278 (1954) and J. Amer., Chem. Soc., 77,3604 (1955)) prepared phenyl, 3-tolyl, 4-tolyl and 4-dimethylaminephenyl derivatives with yields above 81%. Subsequently Beachell and Butter (Inorg. Chem, 4,1133 1965) described the synthesis of the Cp2Ti(3-CF3C6H4)2 and CP2Ti(4-XC6H4)2 derivatives where X=OCH3, F, Cl, Br, CF3) using the same synthesis path. The preparation of diaryl titanocene derivatives by reaction with aryl lithium was again published by Liu et al. in J. Huaxue Tongbao, 10, 26, (1984).
The use of lithium compounds involves the use of very volatile solvents, very low temperatures (xe2x88x9270xc2x0 C.), extremely humidity sensitive reactants and pyrophoric products, which implies an important risk and complexity in the preparation of diaryl titanocene derivatives at industrial scale.
On our side, we have discovered that, surprisingly, the bis(aryl) derivatives of titanocene can be easily prepared by the reaction of titanocene dichloride with the corresponding Grignard derivative. This method substantially enhances safety, reproducibility, yield and cost of the method which is carried out via lithium compounds.
The procedure of this invention is characterised by the use of an organo magnesium for the manufacturing of compounds which have the following formula: 
where:
L, which can be equal or different one from the other, are cyclopentadiene, or pentamethylcyclopentadiene; preferably at least one L is cyclopentadiene; R1, R2, R3, are equal or different from one another, are selected from a group consisting of: hydrogen, alkyl group of 1 to 4 carbon atoms, OR4 where R4 is an alkyl group of 1 to 4 carbon atoms; at least one of the R1, R2 or R3 is hydrogen.
The procedure for the preparation of said titanocenes is characterised by the following steps:
Preparation of the Grignard reagent by reaction of magnesium metal with a compound with the formula (II): 
BrC6H4R, where R1, R2 and R3 have already been defined and Br is bromide, in a polar solvent such as tetrahydrofuran;
b) Reaction of the Grignard reagent in solution with titanocene dichloride in a 2:1 ratio;
Precipitation with a non-polar solvent, such as cyclohexane, of the chlorobromomagnesium salts synthesised in the reaction medium and filtration of the same, obtaining a solution of the compound (I).
Preferably the process according to the following invention refers to compounds which have the formula III 
where:
L, which can be equal or different one from the other, are cyclopentadiene, or pentamethylcyclopentadiene; preferably at least one L is cyclopentadiene; OR4 is an alcoxyle group, containing from 1 to 4 carbon atoms.
The advantages posed by this method respect of those described in the preceding state of art, are the use of less volatile solvents, reaction temperatures between 0 and 70xc2x0 C., cheaper and not so humidity sensitive reactants, which makes operation more simple and safe, and easy to be carried out at an industrial scale. Preferably the solvents used are liquid with boiling points higher than or equal to 65xc2x0 C.
Specific examples of the compounds prepared are: bis(4-methoxyphenyl) bis(cyclopentadienyl) titanium, bis(3-methoxyphenyl) bis(cyclopentadienyl) titanium, bis(4-etoxyphenyl) bis(cyclopentadienyl) titanium, bis(3-etoxyphenyl) bis(cyclopentadienyl) titanium, bis(4-methylphenyl) bis(cyclopentadienyl) titanium, bis(phenyl) bis(cyclopentadienyl) titanium, bis(4-ethylphenyl) bis(cyclopentadienyl) titanium, bis(3-ethylphenyl) bis(cyclopentadienyl) titanium, bis(4-butylphenyl) bis(cyclopentadienyl) titanium, bis(3-butylphenyl) bis(cyclopentadienyl) titanium, bis(3-ethyl,4-methylphenyl) bis(cyclopentadienyl) titanium, bis(4-methoxyphenyl) (cyclopentadienyl) (pentamethylcyclopentadienyl) titanium, bis(3-methoxyphenyl) (cyclopentadienyl) (pentamethylcyclopentadienyl) titanium, bis(4-etoxyphenyl) (cyclopentadienyl) (pentamethylcyclopentadienyl) titanium, bis(3-etoxyphenyl) (cyclopentadienyl) (pentamethylcyclopentadienyl) titanium, bis(4-methylphenyl) (cyclopentadienyl) (pentamethylcyclopentadienyl) titanium, bis(phenyl) (cyclopentadienyl) (pentamethylcyclopentadienyl) titanium, bis(4-ethylphenyl) (cyclopentadienyl) (pentamethylcyclopentadienyl) titanium, bis(3-ethylphenyl) (cyclopentadienyl) (pentamethylcyclopentadienyl) titanium, bis(4-butylphenyl) (cyclopentadienyl) (pentamethylcyclopentadienyl) titanium, bis(3-butylphenyl) (cyclopentadienyl) (pentamethylcyclopentadienyl) titanium, bis(3-ethyl,4-methylphenyl) (cyclopentadienyl) (pentamethylcyclopentadienyl) titanium, bis(4-methoxyphenyl) bis(pentamethylcyclopentamethyl) titanium, bis(3-methoxyphenyl) bis(pentamethylcyclopentamethyl) titanium, bis(4-ethoxyphenyl) bis(pentamethylcyclopentamethyl) titanium, bis(3-ethoxyphenyl) bis(pentamethylcyclopentamethyl) titanium, bis(4-methylphenyl) bis(pentamethylcyclopentamethyl) titanium, bis (phenyl) bis(pentamethylcyclopentamethyl) titanium, bis(4-ethylphenyl) bis(pentamethylcyclopentamethyl) titanium, bis(3-ethylphenyl) bis(pentamethylcyclopentamethyl) titanium, bis(4-ethylphenyl) bis (pentamethylcyclopentamethyl) titanium, bis(3-butylphenyl) bis(pentamethylcyclopentamethyl) titanium, bis(3-ethyl,4-methylphenyl) bis (pentamethylcyclopentamethyl) titanium.
The products prepared by the method described in this invention are obtained with quantitative yields and with a purity of  greater than 97%.
An additional advantage of this procedure is that the titanocene derivative is obtained in solution at an adequate concentration for its direct use in polymerisation or hydrogenation reactions. The solutions of bis(aryl) derivatives are stable at room temperature for long periods of time.
In the procedure described in this invention the reaction with the titanocene dichloride is carried out in the same reactor in which the intermediate Grignard derivative has been synthesised, not being necessary to isolate it, which simplifies and eases the operation.
Below are some explanatory examples of the procedure subject matter of the invention which evidence the advantages of the method compared to those described in the preceding state of art. These examples are not intended as limitations of the invention: